When paints are applied manually or automatically to objects, a substream of the paint, which generally contains both solid bodies and/or binding agents as well as solvents, is not applied to the object. This substream is known amongst experts as “overspray”. The terms overspray, overspray particles or overspray solids will always be used below to refer to a disperse system, such as an emulsion or suspension or a combination thereof. The overspray is taken up by the air stream in the paint booth and supplied for separation so that, if required, the air can be conducted back to the coating booth after suitable conditioning.
Particularly in plants with a relatively high paint consumption, for example in plants for painting vehicle bodies, wet separation systems are preferably used. In commercially known wet separators, water flows together with the booth exhaust air coming from above to a nozzle accelerating the air stream. A swirling of the through-flowing booth exhaust air with the water takes place in this nozzle. In this procedure, the overspray particles pass largely into the water so that the air exiting the wet separator has been substantially cleaned and the paint overspray particles reside detackified in the water. They can then be recovered from this or disposed of.
In known wet separators, a relatively high amount of energy is used to circulate the very large quantities of water required. Treating the rinsing water is costly due to the elevated use of paint-binding and detackifying chemicals and the disposal of paint sludge. Furthermore, owing to the intensive contact with the rinsing water, the air absorbs a high amount of moisture which, in recirculating-air mode, in turn results in a high energy consumption for treating the air.
In contrast, in commercially known devices of the type mentioned at the outset, a dry separation process is used. Particularly established in this regard are electrostatically operating separators in which the paint overspray is guided past a separating surface and separated there due to the overspray particles being ionised by an electrode device and migrating to the separating surface as a result of the electrical field established between the separating surface and the electrode device. The paint overspray particles adhering to the separating surface can then be stripped from this, for example mechanically, and transported away.
The cleaning effect of such separators is indeed very good. However, for continuous operation, it must always be ensured that a sufficiently strong electrical field can be established between the separating surface and the electrode device, which is only possible up to a certain thickness of the paint overspray layer on the separating surface since such a layer has an insulating effect. However, the necessary continuous removal of the paint overspray from the separating surface is associated with high structural costs and can be prone to faults. Overspray may moreover react, harden or dry on the separating surface so that it can no longer be removed by simply being stripped from the separating surface. The energy costs for such separators are moreover relatively high.
An object of the present invention, therefore, is to provide a method, a separating device and a plant of the type mentioned at the outset, which take these problems into account.